1. Field of the Invention
The present invention relates to an optical communication apparatus, an optical wavelength multiplexing transmission system, an optical path failure detection method, an optical path failure detection program, and a program storage medium.
2. Description of Related Art
In recent years, as disclosed in “Optical Transmission System” of Japanese Unexamined Patent Application Publication No. 2006-345070, an optical wavelength multiplexing apparatus for effectively reducing optical repeat loss while extending the optical amplification band has been developed. The optical wavelength multiplexing apparatus has the configuration including a Raman amplifier for performing Raman amplification to optical signals using strong excitation light placed in the previous stage of an optical amplifier such as an Erbium-Doped Fiber Amplifier (EDFA). FIG. 3 is a block diagram illustrating the system configuration of an optical wavelength multiplexing transmission system using the optical wavelength multiplexing apparatus of a related art. In the configuration illustrated in FIG. 3, optical wavelength multiplexing apparatuses 1A and 2A are connected to oppose each other via optical transmission lines 50 and 51. An optical wavelength multiplexing apparatus is exemplified hereinafter as the related art and exemplary embodiment of the present invention. The optical wavelength multiplexing apparatus is included in the optical communication apparatus of the present invention.
In the optical wavelength multiplexing transmission system illustrated in FIG. 3, the optical wavelength multiplexing apparatuses 1A and 2A each include a reception unit and a transmission unit. The reception unit of the optical wavelength multiplexing apparatus 1A is composed of a Raman amplifier 10 and an optical amplifier 11, which are connected in cascade via an optical fiber 15. The transmission unit of the optical wavelength multiplexing apparatus 1A is composed of an optical amplifier 13. Further, the reception unit of the optical wavelength multiplexing apparatus 2A is composed of a Raman amplifier 20 and an optical amplifier 21, which are connected in cascade via an optical fiber 25. The transmission unit of the optical wavelength multiplexing apparatus 2A is composed of an optical amplifier 23.
In the optical wavelength multiplexing apparatuses 1A and 2A of FIG. 3, the reception units for receiving optical signals from each of the opposing apparatuses monitor the flatness of main signals (optical wavelength multiplexed signals) respectively output from the optical amplifiers 11 and 21, which are connected in the subsequent stages, and feed back to the optical amplifiers 11 and 21, so as to control to flatten the output spectrum of the main signals (optical wavelength multiplexed signal). Similarly, in the transmission unit for receiving the optical signals from another path of each of the optical wavelength multiplexing apparatuses 1A and 2A and transmitting the optical signals to the respective opposing apparatuses, by monitoring the flatness of main signals (optical wavelength multiplexed signals) respectively output from the optical amplifiers 13 and 23, which are connected in the subsequent stages, and feeding back to the optical amplifiers 13 and 23, the control to flatten the output spectrum of the main signals (optical wavelength multiplexed signal) is performed.
Further, the optical wavelength multiplexing apparatuses 1A and 2A respectively include supervisory signal transmission and reception units 14 and 24. The supervisory signal transmission and reception units 14 and 24 transmit and receive an OSC (Optical Supervisory Channel) signal to and from the optical amplifiers 11 and 21 which compose the reception unit for receiving the optical signals from respective opposing apparatuses, and the optical amplifiers 13 and 23 which compose the transmission unit for transmitting the optical signals to the respective opposing apparatuses. An OSC signal, i.e., a supervisory signal, is used as a control signal between the optical wavelength multiplexing apparatuses 1A and 2A.
In the event of a failure such as a disconnection of an optical fiber in the optical transmission line 50, for example, in the system configuration as in FIG. 3, a loss of main signal alarm is generated in the optical amplifier 11, and a loss of supervisory signal alarm is also generated in the supervisory signal transmission and reception unit 14 which is monitoring signals from the optical amplifier 11.
Moreover, the supervisory signal transmission and reception unit 14 performs APR (Automatic Power Reduction) control (the control to reduce the optical output signal level to a predetermined level in advance) defined in the ITU-T G.664 standard, and transmits the OSC signal for directing to carry out the APR control to the optical wavelength multiplexing apparatus 2A which is the opposing apparatus via the optical amplifier 13 of the transmission unit. In response to the OSC signal, the supervisory signal transmission and reception unit 24 in the optical wavelength multiplexing apparatus 2A performs the APR control directed by the OSC signal to reduce the output level of the optical signal to the optical transmission line 50.
By performing the APR control, the output level of the optical signal shifts to the low-output-level state, thereby reducing the influence on the worker when performing the recovery operation of the optical transmission line 50.
As mentioned above, in the optical wavelength multiplexing apparatus of the related art as illustrated in FIG. 3, if a failure such as a disconnection in an optical fiber is generated in the optical transmission line 50, and an input optical signal is blocked, the supervisory signal transmission and reception unit 14 of the optical wavelength multiplexing apparatus 1A on the receiving side detects the loss of supervisory signal, and also performs the APR control defined in the ITU-T G.664 in response to the information of the loss of main signal from the optical amplifier 11. However, the blocked state of the input optical signal is generated in a similar manner not only when a failure occurs in the optical transmission line 50 between the optical wavelength multiplexing apparatuses 1A and 2A, but for example when a failure occurs in the optical fiber 15 which connects the Raman amplifier 11 and the optical amplifier 11 in cascade.
That is, in FIG. 3, if a failure occurs in the optical fiber 15 between the Raman amplifier 10 and the optical amplifier 11, a loss of main signal (optical wavelength multiplexed signal) alarm is generated in the optical amplifier 11, and a loss of supervisory signal alarm is generated in the supervisory signal transmission and reception unit 14. Thus the supervisory signal transmission and reception unit 14 performs the APR control in a similar way as the abovementioned case of a failure in the optical transmission line 50. As the result, the state shifts to the state of reducing the output level of the optical amplifier 23 of the optical wavelength multiplexing apparatus 2 on the opposing apparatus side.
As described above, in the optical wavelength multiplexing apparatus of the related art, for the circuit configuration having multiple optical circuits connected in cascade as the communication system of optical signals like the Raman amplifier and the optical amplifier with the amplification function for optical signals that are connected in cascade, even if a failure occurs in the optical fiber in the apparatus including multiple optical circuits connected in cascade, the failure point cannot be identified. Therefore, such failure is processed in a similar way as the failure in the optical transmission line connecting between the opposing apparatuses. Thus there is a possibility that the replacing operation of the optical transmission line where no failure occurs is performed and causes a problem that substantially delays the recovery.